color mask not exporting in Final Cut Pro

Hello.



I'd like to use a color mask to hide unwanted colors and shapes in Final Cut Pro, and I found out the color mask will not be exported when I try.


This is the clip I'd like to export. I've used color mask, and screen captured the scene.



(sorry for bad resolution)



This is the clip I exported. It's the same clip, but you can see black waterdrops are not hidden.




I've exported it through Apple Prores 4444.

Is there any way I can export this right?


Thank you.